Structure-property correlation of submerged-arc and gas-metal-arc weldments in HY-100 steel
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INTRODUCTION
HY-100 is a low carbon low alloy steel quenched and tempered to achieve a yield strength of 690 MPa. Like HY80, ~ the quenched and tempered microstructure of HY-100 steel consists of a bainitic-martensitic duplex structure. Essentially no information on the microstructure-fracture resistance correlation exists in the open literature on HY100. However, some information on similar steels, such as HY-80 and HY-130, should be relevant. A considerable research effort on QT35 (the British equivalent of HY-80) took place in the early 1970's at the Cranfield Institute of Technology, United Kingdom. The results of Kellock e t al.2 are representative of this research. They report that the best toughness in these steels is achieved when the microstructure consists of a fine autotempered martensite. This is achieved by restricting the heat input to a maximum of 2.1 kJ/mm coupled with preheat and interpass temperature controlled at about 393 to 423 K (120 to 150 ~ Higher heat inputs will produce lower cooling rates that degrade the fracture resistance. 3 Most of the results both from the Cranfield and the Navy's development programs are still under some restriction and thus cannot be referenced herein. In a recent publication, Challenger et al. 4 have shown by careful transmission electron microscopy (TEM) that it is P. DEB, formerly Adjunct Research Professor with the Materials Engineering Group, Naval Postgraduate School, is Metallurgical Engineer, APTECH Engineering Services Inc., Palo Alto, CA 94303. K.D. CHALLENGER is Associate Professor, Materials Engineering Group, Mechanical Engineering Department, Naval Postgraduate School, Monterey, CA 93943. A.E. THERRIEN, formerly Graduate Student at NPS, is LCDR, U.S. Navy. Manuscript submitted May 2, 1985. METALLURGICAL TRANSACTIONS A
necessary to have overlapping weld beads in GMAW welds of HY-130 in order to produce the required microstructure. In the absence of the thermal cycle created by successive weld beads, the tempering of the martensite was incomplete, resulting in a HAZ hardness that gave reason for concern with respect to the fracture resistance of any such region of a multipass weld. As a result of this work on HY-130, they concluded that TEM was required to characterize the fine microstructures present in welded regions. What appeared by optical metallography to be similar microstructures were often quite different when examined by TEM. We illustrate this point in this present paper. The role of inclusions in the transformation of austenite in this class of steels is still unclear. It has been shown, however, that a lower volume fraction of inclusions will increase these steels' resistance to microvoid coalescence, and that the best resistance to brittle fracture occurs with the fine autotempered martensitic microstructures. A significant portion (about 50 pct) of the cost of ship construction is attributed to welding operations. Hence, the cost of ship construction could be substantially reduced by the cost effectiveness of a highly automated, hig
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